Modern aircraft designs can include unstable airframe configurations such as the X-29 aircraft and can include multi-control surfaces utilized for the foregoing function. Due to the location of the center of gravity of such an aircraft, there is inherent instability which must be carefully attended to by a computer-aided flight control system. Feedback in the flight control system is provided with normal acceleration and pitch rate parameters, derived from accelerometers and gyros. This feedback data is supplied to a servo system which is intended to stabilize the aircraft.
In multi-control surface high performance aircraft such as the canard-equipped X-29, the craft is inherently unstable, and dependence upon conventional flight control system technology has raised the problems of attaining stability margin while minimizing the sensitivity of the flight control system to noise. At high operational speeds, these factors detract from the effectiveness of such an aircraft.